I would do it with keyframes but there is another way. If you place an adjustment layer above the clip you can apply a grade to the adjustment layer and then fade that layer out or in over the shot.
There are times when that simple approach will work. For complexity, keyframes are your friend. I would not use that method for power windows but it might be a way to add a complex grade overlay to a graded sequence. I’ve used to it slowly transition a scene to a high contrast black & white.